Carrier film and process for producing the same

ABSTRACT

The present invention provides a carrier film in which a cover resist layer made of epoxy acrylate resin including a fluorene skeleton is formed on a heat-resistant resin film including a conductive wiring pattern. The carrier film has heat resistance, moisture resistance, and close contact property, as well as chemical resistance in a plating process or the like, and does not warp because contraction in resin hardening is small.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a carrier film into which asemiconductor device is suitably mounted at high-density and to aprocess for producing the same.

2. Description of the Related Art

As a carrier film into which the semiconductor device is mounted, thereis a conventionally known carrier film as disclosed in pages 727 to 732of the 46th Electric Component & Technology Conference, for example.FIG. 1 is a schematic sectional view showing such a construction. InFIG. 1, tape matrix 34 comprising a copper wiring pattern 31, a baselayer 32 made from polyimide film, and a bonding layer 33 made fromthermoplastic polyimide film is provided with a bump 35 for electricalconnection to a chip, and a cover resist layer 37 having openings 36 forelectrical connection to a substrate to be mounted is defined on thecopper wiring pattern 31.

In the carrier film having the above construction, quality of materialand forming conditions of the cover resist layer 37 have a greatinfluence on process margin and reliability in assembly of thesemiconductor device. Properties required for the cover resist layer 37are heat resistance, moisture resistance, close-contact property,chemical resistance in a plating process or the like, and smallercontraction in hardening of resin to prevent warping of the carrierfilm. Furthermore, in order to keep up with refinement of openings 36due to increased number of pins in the semiconductor device, it isdesirable to form the cover resist layer 37 in exactly the same exposureand developing process as those for a normal photoresist.

Epoxy acrylate resin or polyimide resin disclosed in Japanese PatentApplication Laid-open No. 6-230571 or Japanese Patent ApplicationLaid-open No. 8-50353, for example, is known as material of the coverresist. However, the conventional epoxy acrylate resin does not havesufficient heat resistance, causing degradation in insulation due to sagof pattern or carbonization in an assembling process of thesemiconductor device. Further, the conventional epoxy acrylate resindoes not have sufficient moisture resistance and chemical resistance andcan not form a reliable semiconductor device. On the other hand, thepolyimide resin has sufficient heat resistance of 300° C. or more.However, the polyimide resin contracts largely at the time of hardeningto cause warping, and is necessary to be heated at temperature of ashigh as 300° C. or more for hardening, such heat degrading the bondinglayer 33. For the above reasons, it is very difficult to apply thepolyimide resin to the carrier film.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a carrier film inwhich a cover resist layer is formed on a heat-resistant resin filmincluding a conductive wiring pattern, the cover resist layer havingheat resistance, moisture resistance, close contact property, chemicalresistance in a plating process or the like, and does not warp becausecontraction in resin hardening is small.

To achieve the above object of the present invention, there is provideda carrier film in which a cover resist layer made of epoxy acrylateresin including a fluorene skeleton is formed on a heat-resistant resinfilm including a conductive wiring pattern. Furthermore, the carrierfilm which is remarkably flexuous and facilitates assembly of asemiconductor device can be obtained by forming the cover resist layermade of the epoxy acrylate resin including the fluorene skeleton byheating at temperature in a range of 180° C. to 260° C. for hardening.

Because the epoxy acrylate resin including the fluorene skeleton used inthe present invention has photosensitivity, a through hole can be formedin a photo process like in a case where normal resist material is used.Also, the hardened film has heat resistance of 300° C. or more andcontraction of the film is small when hardened, thereby preventingwarping of the carrier film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a construction of a conventionalcarrier film;

FIGS. 2A to 2E are sectional views showing a process for producing acarrier film according to an embodiment of the present invention inorder of step;

FIG. 3 is a diagram showing an example of a structure of a semiconductordevice using the carrier film according to the present embodiment; and

FIG. 4 is a graph showing a relationship between a hardening temperatureand a fracture elongation rate in formation of a cover resist layer.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be explained belowwith reference to accompanying drawings. FIG. 3 is a sectional viewshowing a semiconductor device assembled using a carrier film accordingto the embodiment of the present invention. FIGS. 2A to 2E are sectionalviews showing a process for producing the carrier film according to theembodiment of the present invention in order of step.

An electrode 12 connected to an internal circuit is formed on a surfaceof a semiconductor substrate 11, and a carrier film 10 is bonded to atop of the semiconductor substrate 11. The carrier film 10 includes abonding layer 3 as its lowermost layer, and a base layer 2 is formed onthe bonding layer 3. A wiring pattern 5 made of copper and formed bypatterning a copper foil 1 is provided on the base layer 2.

A bump 7 connected to the wiring pattern 5 is provided through the baselayer 2 and the bonding layer 3. A cover resist 9 is formed to cover thebase layer 2 and the wiring pattern 5, and openings 8 are provided atappropriate positions of the cover resist 9 on the wiring pattern 5.

In the present embodiment, the cover resist 9 is made of epoxy acrylateresin including a fluorene skeleton. As the epoxy acrylate resinincluding the fluorene skeleton, material represented by the followinggeneral formula (1) is preferably used. ##STR1##

In formula (1), R represents a hydrogen atom or a low-rank alkyl group,n represents an integral number from 0 to 20, and --Ar-- represents adivalent group represented by a following formula (2). R in a formula(II) also represents the hydrogen atom or the lower alkyl group like inthe formula (1). ##STR2##

Use of the material represented by the formula (1) for an opticalpurpose is disclosed in the Japanese Patent Application Laid-open No.4-292611.

It was found that the epoxy acrylate resin including the fluoreneskeleton represented by the formula (1) has excellent heat resistance,moisture resistance, and chemical resistance, and is flexuous so that itcan be formed on a film, as compared with conventional epoxy acrylateresin. Especially, it was found that the epoxy acrylate resin includingthe fluorene skeleton represented by the formula (1) forms a remarkablyflexuous film, if a hardening temperature is set in a range of 180° C.to 260° C.

Next, a process for producing the carrier film of the present embodimentwill be described with reference to FIGS. 2A to 2E. First, as shown inFIG. 2A, the bonding layer 3 for mechanical bonding to semiconductorelements is provided on one face of the base layer 2 made of polyimideresin or the like. On the other face of the base layer 2, the copperfoil 1 for forming the wiring pattern is provided.

Then, as shown in FIG. 2B, the copper foil 1 is etched into apredetermined shape in a photo-lithography process and the like to formthe copper wiring pattern 5.

Next, as shown in FIG. 2C, a through hole 6 is formed using a carbondioxide laser and the like, and as shown in FIG. 2D, the bump 7 isformed for an electrical connection to the semiconductor element, byfilling the through hole 6 with metal by plating.

Further, as shown in FIG. 2E, the epoxy acrylate resin including thefluorene skeleton is coated on an entire face of the copper wiringpattern 5 and an entire exposed face of the base layer 2 in aspin-coating process, a die-coating process, a curtain-coating process,a print process, or the like, for example, and dried to form a coat.Exposure is carried out through a mask, and developing is conducted, toobtain a cover resist 9 having openings 8. Finally, the cover resist 9is hardened by heating, to obtain the carrier film 10 of the presentinvention.

By mechanically bonding the carrier film 10 to the semiconductorsubstrate 11 through the bonding layer 3, the electrode 12 on thesemiconductor substrate is electrically connected to the bump 7, asshown in FIG. 3. In the opening 8, a solder ball 13 is mounted, forexample, to obtain a semiconductor device 14 with excellent reliability.

In the assembling process of the semiconductor device 14, it isdesirable to use the carrier film 10 in a shape of reel, in order toimprove productivity. Therefore, the cover resist layer 9 which formsthe carrier film 10 is desirably flexuous for easier handling. As aresult of study, it was found that the cover resist layer 9 made of theepoxy acrylate resin including the fluorene skeleton forms a film whichis remarkably flexuous, when the film is formed by heating attemperature in a range of 180° C. to 260° C. for hardening.

FIG. 4 is a graph showing a relationship between hardening temperatureand fracture elongation rate in formation of the cover resist layer 9.The fracture elongation rate is an elongation rate in a moment offracture caused by pulling both ends of a film. The larger the fractureelongation rate is, the more flexuous the film is judged to be. As canbe seen from FIG. 4, if hardening temperature is set in a range of 180°C. to 260° C., the cover resist layer 9 can be obtained which isremarkably flexuous and has the fracture elongation rate of 10% or more.

Next, evaluation result of a carrier film will be explained, the carrierfilm being produced by forming the cover resist layer made of the epoxyacrylate resin including the fluorene skeleton on the heat-resistantresin film including the conductive wiring pattern.

First, as shown in FIG. 2A, tape matrix 4 was prepared which comprisesthe copper foil 1, the base layer 2 made from the heat-resistant resinfilm such as polyimide and the like, and the bonding layer 3 made of thethermoplastic polyimide and the like.

Next, the copper foil 1 was etched into the predetermined shape in thephoto-lithography process to form the copper wiring pattern 5 (FIG. 2B).

Then, the through hole 6 was defined in the base layer 2 and the bondinglayer 3 in a laser working process (FIG. 2C), and the through hole 6 wasfilled with metal by plating, to obtain the bump 7 for electricalconnection to the semiconductor device (FIG. 2D).

Further, the epoxy acrylate resin including the fluorene skeleton wascoated on the entire faces of the copper wiring pattern 5 and the baselayer 2 in the spin-coating process, and was dried at temperature of 75°C. for 20 minutes. And, exposure of 600 mJ/cm² and dip developing forthree minutes in aqueous solution including 1% of sodium carbonatedecahydrate were carried out, to obtain the cover resist layer 9 havingopenings 8.

Finally, by heating the cover resist layer 9 for hardening attemperature of 230° C. for 30 minutes, the carrier film 10 was formed(FIG. 2E).

The cover resist layer 9 made of the epoxy acrylate resin including thefluorene skeleton had chemical resistance enough to prevent any problemin applying nickel or gold plating to the openings 8. Also, the coverresist 9 had heat resistance of 300° C. or more and excellent moistureresistance, having absorption rate of as low as 0.7%. As a result, thecover resist layer 9 did not suffer from problems of absorption and lackof heat resistance in the assembling process of the semiconductordevice, and the carrier film 10 with excellent reliability could beobtained. And, contracting rate in hardening was 6% which was remarkablysmall as compared with contracting rate of 50% of the polyimide resin,and warping did not caused in the carrier film 10.

The present invention is not limited to the above embodiment, but can bemodified variously. For example, the epoxy acrylate resin including thefluorene skeleton may be coated in the die-coating process, thecurtain-coating process, or the print-coating process instead of thespin-coating process. Any of the above coating processes provides thecarrier film with excellent quality and reliability like in the aboveembodiment.

The carrier film of the present invention is obtained by forming thecover resist layer made of the epoxy acrylate resin including thefluorene skeleton on the heat-resistant resin film including theconductive wiring pattern. Therefore, the carrier film does not warp,and has excellent heat resistance, moisture resistance, and chemicalresistance. By using this carrier film, the semiconductor device withexcellent reliability can be formed.

Furthermore, in the process for forming the carrier film, by forming thecover resist layer made of the epoxy acrylate resin including thefluorene skeleton by heating at temperature in a range of 180° C. to260° C. for hardening, it is possible to obtain the carrier film whichis remarkably flexuous and can be handled easily in the assemblingprocess of the semiconductor device.

What is claimed is:
 1. A carrier film comprising:a heat-resistant resin film including a conductive wiring pattern; and a cover resist layer made of epoxy acrylate resin including a fluorene skeleton and formed on said heat-resistant resin film.
 2. A carrier film according to claim 1 wherein said carrier film has heat resistance of at least 300° C.
 3. A carrier film according to claim 1, wherein said epoxy acrylate including a fluorene skeleton is represented by the formula (1) ##STR3## wherein R represents a hydrogen atom or a lower alkyl group, n represents an integer from 0 to 20, and --Ar-- represents a divalent group represented by the structure (2) ##STR4## wherein R represents a hydrogen atom or a lower alkyl group. 